Power amplifiers (PAs) have many important applications in our electronics today, one of which is the application of power amplifiers in radio frequency transmitters, where a low-power signal is amplified into a larger signal of significant power for driving an antenna of a transmitter. Power amplifiers are one of the weakest links in the transmit signal chain. Many new PA architectures have been developed or rediscovered over the last years to improve the linearity, efficiency, bandwidth, and output power.
Power amplifiers have many classes, such as Class A, AB, B, C, E, or F amplifiers. Class A power amplifiers are the least efficient. Power amplifiers use Class AB, B or C configurations where the power driving transistor is on for a smaller fraction respectively of the complete cycle compared to class A, to improve efficiency. FIG. 1 shows illustrative current waveforms for Class A, AB, B, and C amplifiers. These amplifiers' efficiency depends heavily on the control of the current waveform with respect to the voltage waveform in order to minimize power dissipation. However, solutions for controlling the current waveform have been insufficient to achieve optimal efficiency.
Overview
Power efficiency is an important design requirement of power amplifiers. To improve power efficiency, a solution proposed in this present disclosure includes an all-digital zero-voltage switching apparatus for directly driving a switching power amplifier through a desired current pulse shape. The apparatus includes a digital engine and a digital-to-analog converter (DAC). The digital engine processes baseband data and generates a digital output. The digital output of the digital engine drives the DAC to generate a digitally controlled current output having that desired current pulse shape. The digitally controlled current output is used to directly drive the switch power amplifier to improve power efficiency. The digitally controlled current output comprising digitally generated current pulses is controlled accurately by the digital engine and the DAC, and thus allows the switching power amplifier to operate optimally with higher power efficiency than conventional power amplifiers.